Cosmic rays from the ankle to the cutoff

Abstract

Recent advances in measuring and interpreting cosmic rays from the spectral ankle to the highest energies are briefly reviewed. The prime question at the highest energies is about the origin of the flux suppression observed at E 4 · 10 19 eV. Is this the long awaited GZK-effect or the exhaustion of sources? The key to answering this question will be provided by the largely unknown mass composition at the highest energies. The high level of isotropy observed even at the highest energies challenges models of a proton dominated composition if extragalactic magnetic fields are on the order of a few nG or less. We shall discuss the experimental and theoretical progress in the field and the prospects for the next decade. RésuméRayons cosmiques de la chevilleá la coupure Les avancées récentes concernant les mesures et l'interprétation des rayons cosmiques, de la caractristique spectrale appelé cheville jusqu'aux plus hautesénergies, sont briévement revues. Aux plus hautesénergie, la question principale concerne l'origine de la suppression du flux clairement observée au dessus de 4 × 10 19 eV. Est-ce la prédiction GZK tant attendue ? Ou bien l'épuisement des sources ? La clef qui permettra de répondreà cette question réside dans la composition des rayons cosmiques qui est aujourd'hui largement inconnue aux plus hautesénergies. L'isotropie observée dans la distribution des directions d'arrivées, même aux plus hautesénergies, défavorise les modéles oú les protons dominent la composition si les champs magnétiques extragalactiques sont au niveau de quelques nG ou moins. Nous discuterons les progrés expérimentaux et théoriques du domaine et les perspectives pour la prochaine décennie.

The Pierre Auger Observatory: Selected Results and Future Plans

“…1 (top) [22]. As can be seen, the energy spectra are consistent in normalization and shape if the uncertainties in the energy scale are taken into account.…”

“…On the other hand, if primary particles are heavier nuclei, the flux distribution should be anisotropic in a manner similar (but not identical) to the source distribution at the scale of a few tens of degrees, but all the small-scale structure would be washed out. Note that because of the small propagation distance, at the highest energies the sources are expected to be distributed anisotropically due to the large-scale structure of the Universe [22].…”

“…We shall return to this aspect below. Another notable feature of such classes of models is the requirement of injection spectra being considerably harder Energy (eV) [25,33] (from [22]). The TA-data are fit to a model of extragalactic proton sources, distributed cosmologically according to (1+z) 4.4 and injecting a power-law distribution at the sources according to E −2.39 (blue line).…”

Ultra High Energy Cosmic Rays and Neutrinos

“…2 Hereafter discussing freely propagating UHE nucleons we will always refer only to protons because the decay time of neutrons is much shorter than all other time scales involved [13,14,15].…”

“…The experimental and theoretical study of UHECR have brought several important results, such as [1,2,3]: (i) UHECRs are charged particles, with limits on neutral particles up to 10 19 eV at the level of few percent for photons and well below for neutrinos [4,5,6], (ii) the spectra observed on Earth show a slight flattening at energies around 5 × 10 18 eV (called the ankle), with (iii) a steep suppression at the highest energies around 10 20 eV.…”